The field of the disclosure relates generally to stress sensors, and more specifically to a stress sensor including a bridge circuit configured for stress monitoring.
Many electrical systems are implemented in or include electronic circuits fabricated on semiconductor wafers, including, for example, and without limitation, Silicon wafers. The processing and packaging of semiconductor wafers sometimes introduces mechanical stress on the dice cut from the wafers themselves, due to the sawing operation itself or the subsequent molding process to enclose the dice inside a package. Such stresses may impact performance of the electrical system, its circuits and its structures. For example, post-packaging stress has a notable effect on the precision of analog-to-digital converters, digital-to-analog converters, and voltage reference circuits. Such stresses may further impact the carrier mobility in transistors implemented on the wafer. Accordingly, stress sensors are often incorporated into electronic circuits to characterize mechanical stresses that act on the larger circuit, or system on a chip (SoC).
Conventionally, such sensors include van der Pauw resistor structures or rosette arrangements, for example, in which stresses applied to semiconductor wafers, or substrates, are sensed by variations in capacitance or resistance of particular components of the sensor circuits. Substrates are solid surfaces, or wafers, usually planar, on which an electronic circuit is implemented, and may include, for example, silicon, silicon dioxide, aluminum oxide, germanium, gallium arsenide, indium phosphide, or some combination of one or more of the preceding materials. Rosette arrangements may include, for example, asymmetrical serpentine geometries similar to those used in strain-gauges. These conventional implementations of stress sensors typically require a precision current be supplied to the sensor, as well as a precision readout circuit to poll the stress measurement. Accordingly, implementations of multiple sensors, or arrays, are increasingly complex due to the necessary routing of precision current supplies and precision readout signals for each stress sensor circuit in the array. Some alternative implementations include on-chip current sources; however, such current sources are, in turn, sensitive to the mechanical stresses being measured and may contribute to errors in the measurement. Other implementations include shared current- and voltage-monitoring wiring; however, such implementations generally require multiple measurements, multiple meters, and/or physical switching between current and voltage meters, all of which obfuscate the benefits of the eliminated wires.
It is desirable to have simple stress sensors that are easily operated, e.g., powered and polled, or read, or sensed, and that provide high sensitivity. Further, it is desirable to have stress sensors that are easily arrayed to effect measurements on large structures.